The present invention relates to chemical analysis and, more particularly, to a method for on-line detection of polycyclic aromatic hydrocarbons (PAH) and other fluorescent contaminants in aerosols.
PAH are among the many organic materials that are commonly encountered as trace-level environmental contaminants in effluents associated with incomplete combustion, pyrolysis and other thermal degradation processes. The PAH family, defined as containing hydrocarbon species with three or more fused aromatic rings, includes many compounds suspected of being potent carcinogens. Therefore, identification and determination of emission levels of PAH is important in environmental assessment. Moreover, emission monitoring of PAH compounds is of considerable industrial importance as well, since several industrial processes can be controlled by a fast feedback of PAH composition and concentration.
Several procedures, such as gas chromatography/mass spectrometry (GC-MS), have been developed and applied for obtaining compound specific information for evaluation of PAH contamination. These procedures cannot be applied directly to particulate PAH analysis, because they all involve several sample preparation steps in which the particles are destroyed. The GC-MS methods, in particular, are complicated and expensive; they require state of the art high vacuum equipment and extensive investment of expert analyst's time. It is not cost effective to apply them routinely to samples that may not, in fact contain any relevant levels of PAH. Moreover, the GC-MS methods are not on-line methods for particulate analysis, and cannot be used for obtaining fast feedback which is required for both environmental protection and for industrial process control.
PAH compounds are produced primarily as a result of incomplete combustion of organic matter, and thus are believed to exist in both the vapor phase and the solid phase, as an integral constituent of particulate matter. Because the concentration of such pollutants in most atmospheric samples is very low, and because they are often associated with other contaminants, the identification and quantification of PAH are usually complex, time consuming and often inaccurate because of multistep isolation and determination techniques. This problem is primarily associated with analysis of PAH on aerosol particles, which is considered the most complicated task for classical methods of PAH analysis.
Nevertheless, analysis of PAH on aerosols is of intense interest to both industry and governmental environmental protection bodies. It has been proven that most PAH mass is found onto aerosol particles, rather than in the vapor phase. (This is because of the low vapor pressure of many of these compounds at ambient temperature.) The distribution of PAH as a function of aerodynamic diameter, for coke oven emission, shows that most contamination is associated with particles of diameter of 1-10 .mu.m. The absolute concentration of PAH compounds an air is compound-dependent, and is usually in the range of 0.02-0.2 .mu.g m.sup.-3. Absolute concentration in the vicinity of industrial sites may be ten times higher, and concentrations in the .mu.g m.sup.-3 and higher, of particles having diameters between 10 and 100 .mu.m or more, have been measured close to combustion chimneys.
Most of the currently employed analytical methods for PAH on aerosols involve (a) collection of particulate PAH by drawing a large volume of air through a filter, (b) extraction of the PAH collected on a filter paper with an organic solvent, and (c) chromatographic cleanup and separation followed by (d) identification and quantitation using one or a combination of spectroscopic and chromatographic methods, or mass spectrometry analysis in a high vacuum chamber.
There are a number of analytical difficulties associated with these traditional methods. The real-time analysis of PAH present in ambient air (fumes, coke oven emission, smoke or other gaseous media) cannot be achieved, mainly because of lack of selectivity, sensitivity, and mobility of the analytical instrumentation. Considering the above difficulties, and taking into account that traditional methods do not provide on-line and in-situ results, it follows that there is a widely recognized need for, and it would be highly advantageous to have, a method for real-time, on-line analysis of aerosol particles for PAH.